POV-Ray

User-defined warps would be nice to have, something along the lines of:

warp {
  function { MyFnX(x,y,z) } // function to compute pattern-space x-coordinate from object-space <x,y,z> coordinate
  function { MyFnY(x,y,z) } // ditto for pattern-space y coordinate
  function { MyFnZ(x,y,z) } // ditto for pattern-space z coordinate
}

// a displacement warp:
warp {
  function { x + MyFnX(x,y,z) }
  function { y + MyFnY(x,y,z) }
  function { z + MyFnZ(x,y,z) }
}

Most sample scenes and include files were designed at times when POV-Ray did not to any proper gamma handling, or still used the inferior 3.6 “assumed_gamma” mechanism.

All the scenes and include files should be reviewed, and updated to fit the new 3.7 gamma model.

The primary task will probably be gamma-adjusting literal color values and ambient parameters; I suggest using macros (which ideally should be defined in an include file) to be set according to the #version statement, so the scene/include file could be kept compatible with older versions.

The syntax notation used in the main documentation is different than that used in the quick-reference section. This should be changed for consistency, using the superior quick-reference notation throughout.

pov 3.7 Can not identify the Chinese.I give the texture map filename in chinese,it turns out parse error.

[EDIT: Original title was “radiosity causing black patches when using emission less than 0”]

see attached image for reference.

mountain on left has emission set to -.13 and black patches show up, when emmission set to 0 or greater no patches

changing max_trace or any radiosity settings has no effect

setting no_radiosity on mountain fixed problem as a temp fix

code sample ...

#version 3.7;

#default { finish { ambient 0 } }
#declare rad_lvl = 4;

global_settings {
  assumed_gamma 1
  max_trace_level max(5,rad_lvl*3)
  adc_bailout .007
  ambient_light 0
  radiosity {
   pretrace_start 64/max(image_width,image_height)
   #if(rad_lvl)
    pretrace_end max(2,int(8/rad_lvl))/max(image_width,image_height)
   #else
    pretrace_end 32/max(image_width,image_height)
   #end
   count pow(rad_lvl+1,2)*10
   nearest_count 1
   #if(rad_lvl) error_bound 1/rad_lvl #end
   low_error_factor max(.4,(8-rad_lvl)/10)
   recursion_limit 1
   gray_threshold .25
   brightness 1
   max_sample 1
   normal on
   media off
   always_sample off
   minimum_reuse min(.008,8/max(image_width,image_height))
   maximum_reuse .1
   adc_bailout .02
  }
}

#declare sunC = rgb <1, 1, .9925>; // actual D65 standard illuminant
#declare SkyC = rgb <.3195, .5745, .8805>;
#macro GammaAdj(C,G) rgb <pow(C.red,G),pow(C.green,G),pow(C.blue,G)> #end

light_source {
  50000*y
  sunC*1.06
  area_light <-300, 0, -300>, <300, 100, 300>, 3, 3
  rotate <-28, 0, 14>
  adaptive 0
  circular
}

 sphere { 0, 1
  texture {
   pigment{
    gradient y
    pigment_map{
     [.07 GammaAdj(SkyC,.5)]
     [.2 average pigment_map { [.5 GammaAdj(SkyC,.75)][1 wrinkles turbulence .65 octaves 5 lambda 3 omega .9 color_map { [.2 rgb 1][.5 SkyC] } scale <10, .1, 1>] }]
     [.4 GammaAdj(SkyC,1.15)]
     [.5 GammaAdj(SkyC,1.35)]
    }
    rotate -75*y scale <1, 1, 100>
   }
   finish { diffuse .72 }
  }
  scale 100000
  inverse
 }


#declare Cam_pos = Cam_pos + <0, 20, -40>;
#declare Cam_lkt = Cam_lkt + <0, 10, 50>;
camera {
  location Cam_pos
  direction <0,0,1>
  right 1.33*x
  up y
  sky <0,1,0>
  #if(Cam_agl) angle Cam_agl #end
  look_at Cam_lkt
}

#macro sinai(HillQ)
 #local F = function { pattern { granite poly_wave 4 turbulence .01 lambda 2.1 omega .9 scale 5 translate <.2, 0, 18.08> scale <2, 1, 3> } }
 #local N = function { pigment { crackle ramp_wave turbulence .3 lambda 2.2 omega .76 color_map {[0 rgb 0][1 rgb 1] } scale .07 translate <-.15, -.12, .13> } }
 height_field {
  function HillQ, HillQ { F(x,y,z) + N(x,y,z).grey/47 }
  water_level .05
  clipped_by { box { <0, .05, .3>, <1, 1, 1> } }
  translate <-.5, -.05, -.5>
  rotate 20*y
  texture {
   pigment{ crackle color_map { [0 rgb <161, 107, 71>/255][.25 rgb <193, 132, 93>/255][.35 rgb <218, 163, 123>/255][.45 rgb <212, 153, 112>/255][.55 rgb <222, 166, 125>/255][.65 rgb <236, 178, 124>/255][.75 rgb <220, 154, 102>/255][.85 rgb <160, 121, 103>/255] } turbulence .75 lambda 3 omega .7 scale .1 }
   finish{ diffuse albedo .56 emission -.13 specular .25 roughness .02 brilliance 1.5 metallic 1.3 }
   normal { crackle poly_wave .7 turbulence .4 omega .8 scale <.007, .03, .007> }
  }
  rotate 12*y
  scale <2400, 2000, 3000>*1.5
  translate <1900, 0, 1900>
  scale <-1,1,1>
  no_radiosity
 }
#end


sinai(1600)
plane { y,0 pigment { rgb <1, 1, 1> } }

//courtyard gating not included due to size of code and many external files needed. add anything around <0,0,0> to try to reproduce effect of error

For proper render abort/continue support, radiosity cache data must be written to (or read from) disk even if the user does not explicitly opt to have a sample data file written/read. This feature has temporarily been dropped from 3.7 beta and is still pending re-implementation.

To meet high-reproducibility requirements in conjunction with SMP operation, it may be necessary to extend the 3.6 radiosity cache file format.

With 3.7.0 final, rendering attached files (for Computer Engineering college course),
which renders without issues in povray 3.6.1, fails with following error:

...
==== [Rendering...] ========================================================
povray: backend/lighting/radiosity.cpp:324: virtual void pov::RadiosityFunction::BeforeTile(int, unsigned int): Assertion `(pts >= PRETRACE_FIRST) && (pts <= PRETRACE_MAX)' failed.

Command line:

povray +K0.6500 \
+FN +Q9 +MB1 \
+W600 +H400 \
+AM1 +A0.0 +R2 \
+D +SP32 +EP4 \
+L/usr/share/povray-3.7/include \
+Imain.pov \
+Omain-0.6500.png

Using Arch Linux testing current:
Linux archmidi 3.12.0-1-ARCH #1 SMP PREEMPT Wed Nov 6 09:06:27 CET 2013 x86_64 GNU/Linux

Downstream bug report:
https://bugs.archlinux.org/task/37689

when a prism is differenced with a primitive (cylinder in this case) if sslt is used it causes a seq fault. Reference distribution file logo.inc and the Povray_Logo_Prism definition.

While familiarizing myself with the code, I found some small changes in the solve_cubic function that lead to a significant speedup.

In my experience, “pow” is by far the slowest function in math.h and replacing it with simpler functions usually makes a tremendous impact on the speed (it’s an order of magnitude slower than sqrt/exp/cbrt/log).

solve_cubic has a “pow” function that can be replaced by cbrt (cubic root), which is standard in ISO-C99 and should be available on all systems. Separate benchmarks of solve_cubic function show this change almost doubles the speed and does not lower the accuracy. As solve_cubic is part of the solution of quartic equation, this improves the speed for many primitives. Testing with a scene containing many torus intersection tests (attached below) I still observed almost 10% speedup (Intel, 4 threads, 2 hyperthreaded cores, antialiasing on, 600×600: from 91 to 84 seconds). And this is for a torus, where a lot of time is spent in the solve_quartic and cubic solver is only called once! Similar speedup should be expected for prism, ovus, sor and blob.

I do believe the cubic solver can be done without trigonometry, but that would mean changing the algorithm, introducing new bugs and requiring a lot of testing. However, the trigonometric evaluation can still be simplified (3% speedup in full torus benchmark).

These changes don’t affect the algorithm at all, they are mathematically identical to the existing code, so the changes can be applied immediately. I also included other changes just as suggestions. Every change is commented and marked with [SC 2.2013].

This sadly does not speedup the sturm solver, which uses bisection and regula-falsi and looks very optimized already.

The test scene I used has a lot of torus intersections from various directions (shadow rays, main rays, transmitted rays).

Subsurface Scattering still uses its own rudimentary code to compute illumination from classic light sources; this must be changed to use the standard light source & shadow handling code, to add support for non-trivial light sources (e.g. spotlights, cylindrical lights, area lights), partially-transparent shadowing objects etc.

Subsurface scattering must be made photon-aware.

Near concave edges, radiosity samples may be re-used at a longer distance away from the edge than towards the edge; there is code in place to ensure this, but it only works properly where two surfaces meet roughly rectangularly, while failing near the junction of three surfaces or non-rectangular edges, potentially causing “cross-talk”.

It should be investigated how the algorithm can be improved or replaced to better cope with non-trivial geometry.

Currently, radiosity does not make use of the fact that pertubed normals would theoretically just require a different weighting of already-sampled rays, leading to the following issues:

• Honoring normal pertubations in radiosity leads to an increased number of samples, slowing down sample cache lookup.
• The increased number of samples is generated from a proportionally higher number of sample rays, slowing down pretrace even further.
• Low-amplitude pertubations tend to be smoothed out; “reviving” these is only possible by increasing the general sample density.
• Handling of multi-layered textures with different normal pertubations is currently poorly implemented.

As a solution, I propose to store for each radiosity sample not only the resulting illumination for a perfectly unpertubed normal, but from the same set of sample rays also compute the illumination for an additional set of about a dozen standardized pertubed-normal directions, and interpolate among these when computing the radiosity-based illumination for a particular point that has a pertubed normal.

For backwards compatibility, this method of dealing with pertubed normals in radiosity might be activated by a different value for the “normal” statement in the radiosity block, say, “normal 2”.

The SDL currently provides no way to compute the exact direction of a spline at a given location, even though mathematically this is a piece of cake: The first-order derivative of any spline section gives you the “speed” as a vector function, and is trivial to compute for polynomial splines (which are behind all spline types that POV-Ray supports); the normalized “speed” vector, in turn, gives the “pure” direction.

For exact direction/speed computations, I propose to extend the SDL invocation syntax as follows to allow for evaluating a spline’s derivative:

    SPLINE_INVOCATION:
        SPLINE_IDENTIFIER ( FLOAT [, SPLINE_TYPE] [, FLOAT] )

or

    SPLINE_INVOCATION:
        SPLINE_IDENTIFIER ( FLOAT [, FLOAT] [, SPLINE_TYPE] )

where the second FLOAT will specify the order of derivative to evaluate (defaulting to 0). In order to compute the position, direction, and acceleration of an object traveling along a certain spline, one could then for instance use:

    #declare S        = spline { ... }
    #declare Pos      = S(Time);
    #declare VSpeed   = S(Time,1);
    #declare VAccel   = S(Time,2);
    #declare Dir      = vnormalize(VSpeed);
    #declare Speed    = vlength(VSpeed);
    #declare AccelDir = vnormalize(VAccel);
    #declare GForce   = vlength(VAccel) / 9.81;

Alternatively, a mechanism may be devised to create a spline representing another spline’s derivative; however, it would be debatable whether the syntax should be parameter-like (being an added information that could be overridden again when creating other splines from such a derived spline), or operation-like (converting the spline), and in the latter case how it should affect spline type (and consequently control points); so the spline invocation parameter approach might be more straightforward, with less potential surprises for the user.

The following scene causes a crash:

sphere {
  <0,0,0>, 1
  finish { subsurface { translucency 1.0 } }
}

global_settings {
  subsurface { }
}

When resolution is not specified (neither via POVRAY.INI nor via QUICKRES.INI nor via command line or custom .ini file), random values are displayed for image resolution in the Image Output Options message output. (The actual render will be performed at the default size of 160×120 pixels though.)

When using cutaway_textures in a CSG object that has union children, results are not as expected; instead, surfaces in the union children that have no explicit texture will be rendered with the default texture instead. This is not the case for e.g. difference children.

Example:

#default { texture { pigment { rgb 1 } } }

camera {
  right x*image_width/image_height
  location  <0,1.5,-4>
  look_at   <0,1,0>
}

light_source { <500,500,-500> color rgb 1 }

#declare U = union {
  sphere { <0,-0.1,-1>, 0.3 }
  sphere { <0, 0.1,-1>, 0.3 pigment { color red 1 } }
}

intersection {
  sphere { <0,0,0>, 1 pigment { color green 1 } }
  object { U }
  cutaway_textures
  rotate y*90
}

When declaring U as an intersection instead, the results are as expected, with the surface of the first sphere in U being rendered with the texture defined in the outer intersection.

Using prisms in intersecion or difference CSG objects may cause artifacts in POV-Ray 3.6.2 as well as 3.7.0.beta.34, as demonstrated by the following code:

camera {
  right    -x
  up        y*image_height/image_width
  location  <-24,19,12>
  look_at   <0,0,0>
}

light_source { <100,200,100> color rgb 1 }

plane { y, -2 pigment { color rgb 1 } }


#declare KeyValue = 1.366; // pick any you like

difference {
  prism {
    linear_sweep -0.5,0.5, 4
    
    <-3,20-17>,
    <-3,KeyValue>,
    <-6,-3>,
    <-0,-5>
  }
  intersection {
    cylinder { <-7,-0.51,1>, <-7, 0.51,1>, 4.0 }
    plane { z, KeyValue }
  }
  pigment { color rgb 0.5 } 
}

Apparently the surface of the other object becomes visible when it exactly coincides with a vertex of the prism; probably there is a failure of the inside() test for such values.

Dear PovRay maintainers and developers, congratulations for your great RayTracer!

We think that we have found a bug while we were rendering a piece of cloth.

In this piece of cloth were defined two textures, one for one side and one for the another side:

  texture { mesh_tex0_0 }
  interior_texture { mesh_tex0_1 }

• Please: Look at line 77414 of the attached file “test.pov” to see

these definitions in their original context.

We have found some artifacts in the final rendering, in concrete near some wrinkles,
please, look at the attached file “render_artifacts.tga”, I have painted a big green arrow
near the artifacts, maybe you’ll need to do a zoom to see them more accurately.

They are as though the texture of the other side was painted in the incorrect side.

Fortunately, we have a patch to fix this bug (thanks to Denis Steinemann, he made the
implementation for PovRay 3.5, so I have adapted these changes to release 3.6.1)

Although we have found this bug in the Windows and Linux 3.6.1 releases,
the patch was generated in Linux (using the source code release of “povray-3.6.1”).

To apply this patch, inside the parent folder of the directory “povray-3.6.1” execute:

            patch -p0 < other_side_artifacts.patch

And the “povray-3.6.1” will be patched and you will get a console output like this:

 patching file povray-3.6.1/source/lighting.cpp
 patching file povray-3.6.1/source/mesh.cpp
 patching file povray-3.6.1/source/render.cpp

We don’t know if this “hack” is enough smart to apply in the next release,
but we think that it fixes the bug (the artifacts dissapear).

Best regards and thank you very much for your great RayTracer!